Field of the Invention
The invention lies in the integrated technology field. More specifically, the invention relates to a method and an integrated circuit for increasing an input voltage, in which a charge pump is first of all used to precharge a first capacitor to the input voltage and, in a second step, its stored charge is converted to an increased output voltage.
Particularly in the case of portable electronic appliances such as radios, cellular phones, audio equipment, computers, cameras, and the like, it is frequently desirable to design these appliances to be as small and as light as possible. The number of batteries in one appliance in this case means an undesirably high space requirement and, furthermore, a correspondingly heavy weight as well. On the other hand, the assemblies, which are frequently in the form of an integrated circuit such as memories, amplifiers, etc., frequently require a specific minimum voltage in order to guarantee their functions, for physical reasons. Particularly in the case of dynamic memories such as DRAMs (Dynamic Random Access Memory) which, depending on the type, require a supply voltage of at least 2.5 volts or 3.3 volts, a continuous voltage supply is required in order to avoid the stored data being lost. Some integrated circuits also require two or more different operating voltages, which cannot be derived from a single battery without relatively major complexity.
A single battery cell, for example a NiCd cell, which generally outputs 1.2 to 1.5 volts depending on the type, is often inadequate for the problems mentioned above. This is particularly so when the battery cell has already been partially discharged and its voltage falls further when it is further subjected to a load.
Until now, attempts have been made to solve this problem, for example, by reducing the physical size of the batteries and then connecting two or more relatively small batteries in series in order to produce a higher voltage (input voltage). This has the disadvantage that the space required is still relatively large.
Voltage converters with transformers or the like have been used in the past in order to produce a higher voltage, in particular from a low voltage. However, these operate only with AC voltages and are thus not feasible without additional complexity for battery-powered appliances.
Furthermore, a pump circuit is known, having a charge pump, by means of which the input voltage can, for example, be doubled with acceptable complexity. The charge pump is in this case implemented on the chip of the integrated circuit, with appropriate capacitors being charged by way of MOSFET transistors as electronic switches. A single-stage charge pump has the disadvantage that the voltage cannot be more than doubled, and a relatively large chip area is required for greater current ratings.
A method and an integrated circuit for charge pumping are known from German patent application DE 44 43 690 A1. There, an input voltage is increased to a higher output voltage by way of capacitors that are connected in series.